Jan. 21 (UPI) -- Sen. Kamala Harris announced Monday she is running for president of the United States, an expected announcement in which she enters a growing field of Democratic candidates eager to run against President Donald Trump in 2020.

Harris, California's former attorney general who won a seat to replace longtime Democratic Sen. Barbara Boxer in 2016, said in her nearly 1-minute announcement video that she wanted to bring people together.

"The future of our country depends on you and millions of others lifting our voices to fight for our American values," Harris said in the video posted on Twitter. "That's why I'm running for president of the United States. I'm running to lift those voices; to bring our voices together."

Harris, 54, asked viewers to join her for a campaign event in Oakland on Sunday.

"Let's do this together," she said. "Let's claim our future, our ourselves, for our children and four our country."

Harris is the fourth Democratic woman to officially run for the party's nomination as well as the third female U.S. senator. Massachusetts' Elizabeth Warren and New York's Kirsten Gillibrand announced they established exploratory committees to run for president.

Rep. Tulsi Gabbard, D-Hawaii, also said she's running for president, though she has yet to make a formal announcement. Julian Castro, former U.S. Housing and Urban Development secretary under President Barack Obama, made his bid official Jan. 12.

Harris, 54, confirmed her candidacy Monday morning during an appearance on ABC's Good Morning America.

"I love my country. I love my country," the senator said, explaining why she made her announcement on Martin Luther King Jr. Day. "This is a moment in time that I feel a sense of responsibility to stand up and fight for the best of who we are.

"The thing about Dr. King that always inspires me is that he was aspirational. He was aspirational like our country is aspirational. We know that we've not yet reached those ideals. But our strength is that we fight to reach those ideals. So today, the day we celebrate Dr. King, is a very special day for all of us as Americans and I'm honored to be able to make my announcement on the day we commemorate him," she continued.